JP2015099860A - Optical semiconductor module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor module capable of a high-speed operation by using an optical semiconductor element where light is emitted from or enters into an end face.SOLUTION: An optical semiconductor module comprises: a high-frequency wiring board 25; an optical semiconductor element 1 which is a tabular optical semiconductor element 1 having a crystal growth surface arranged to face the high-frequency wiring board 25 and light entering into or emitted from at least one end face among four end faces; and securing means including gold bumps 42 and an adhesive 41, for electrically connecting and securing the optical semiconductor element 1 to on the high-frequency wiring board 25. The optical semiconductor element 1 has a flow stop part 2 of the adhesive 41 on the crystal growth surface near the end face and is formed to have a length in a direction of an optical axis of light which enters or is emitted longer than a length of the high-frequency wiring board 25.

Description

  The present invention relates to an optical semiconductor module, and more particularly to an optical semiconductor module that is a component of a large-capacity optical communication network.

  The optical semiconductor module is used as a communication light source in an optical transmission module as shown in Patent Document 1, for example. FIG. 1 shows a configuration of a conventional wire-mounted two-channel optical transmitter. The optical transmitter of FIG. 1 includes a DFB type (distributed feedback distributed feedback) laser array 10 shown in (a), and a high-frequency wiring board 20 placed on a subcarrier 30 shown in (b). Are connected by a wire W, and are configured as shown in (c) and (d).

  First, a DFB laser array 10 with a multiplexer (also referred to as a chip) used in the two-channel optical transmitter shown in FIG. The laser array 10 has a semiconductor stacked structure configured as a plurality of regions in the optical axis direction. Each area performs different functions. In FIG. 1A, the laser array 10 includes a region a that becomes a waveguide and a multiplexer portion, and a region b that becomes a DFB semiconductor laser portion. The region a 'normally has the same layer structure as the region a, but has a different layer structure when used as a monitor PD with an electrode attached. In the figure, two DFB lasers are multiplexed by a 2-input 1-output (MMI: multi-mode interference multimode interference type) multiplexer. Also, a DFB laser pad 11 and a multiplexer pad 12 are provided on the crystal growth surface side of each of the regions a and b. The laser array 10 is an edge-emitting device in which light is emitted from the right end surface shown in the drawing, and anti-reflection coatings 13 and 14 are applied to both end surfaces in order to prevent deterioration of element characteristics due to multiple reflection.

  A subcarrier 30 shown in FIG. 1B is provided with a high frequency wiring board 20 for applying a high frequency signal to two DFB lasers. A high frequency line 21 is provided on the high frequency wiring board 20.

  FIGS. 1C and 1D are a top view and a side view of a two-channel optical transmitter on which the laser array 10 is mounted, respectively. The laser array 10 is mounted on the subcarrier 30 using solder or an adhesive. Subsequently, the subcarrier 30 is mounted on the carrier 40 using solder or an adhesive, and each DFB laser and the high-frequency wiring board are connected by a gold wire W.

  In addition to the DFB (distributed feedback distributed feedback) laser array, the optical semiconductor module can be used in other structures (for example, a DFB laser integrated electroabsorption optical modulator (hereinafter referred to as EADFB laser)). FIG. 2 shows a conventional wire-mounted EADFB laser module. In the EADFB laser module, as shown in FIG. 2A, a semiconductor chip 50 having a semiconductor laminated structure in which a region b functions as a DFB semiconductor laser, a region c functions as an EA modulator, and a region a functions as a waveguide and a multiplexer. Can be used. The semiconductor chip 50 shown in FIG. 2A and the high-frequency line substrate 26 placed on the carrier 40 shown in FIG. 2B can be wired with a gold wire W (FIG. 2C).

  As shown in FIG. 1 and FIG. 2, the light source for optical transmission is mounted with the substrate surface of the chip (laser array 10 and semiconductor chip 50) facing down (that is, the crystal growth surface and the pad surface facing up), and high-frequency wiring A structure using wire connection for connecting the plates 20 and 26 and the electrode 11 on the chip is common. However, this configuration has a problem that the band is deteriorated due to the parasitic inductance component of the wire and a problem that heat dissipation is poor because the heat of the active layer on the chip is radiated through the substrate surface of the chip.

JP 2003-207693 A

Tsukada Hiroshi et al., “Problems and Future Prospects of Semiconductor Chip Mounting by Flip Chip Connection”, IEICE Transactions C, Vol. J91-C, no. 11, pp. 509-518, 2008 H. S. Venugopalan et al. , Third International Conference on Solid State Lighting, edited by Ian T. Ferguson, Nadarajah Narendran, Steven P. et al. DenBaars, John C. Carrano, Proc. of SPIE Vol. 5187 (SPIE, Bellingham, WA, 2004), pp. 260-266. Kanazawa Ji et al., "Direct modulation DFB laser for flip chip mounting", IEICE Technical Report, IEICE Technical Report, EMD2010-62, CPM2010-78, OPE2010-87, LQE2010-60 (2010-08) , Pp. 169-174.

  However, as a communication light source, a higher speed is demanded with the recent trend of increasing the communication capacity, and the current technology has solved the above-mentioned problems caused by adopting wire connection. It was hoped that this would be solved. Therefore, as a technology to solve this problem, in the electronic device field, the substrate surface of the chip is raised (that is, the crystal growth surface and the pad surface are down), and gold bumps of about several tens of microns are used instead of wires. A flip chip mounting technique for connecting an on-chip electrode and a high-frequency wiring board has been proposed. At this time, the gap between the chip connected to the flip chip and the high-frequency wiring board is filled with an adhesive such as an epoxy resin (also referred to as an underfill material), thereby reducing the difference in thermal expansion coefficient between the chip and the high-frequency wiring board. Patent Document 1).

  In the case of an optical semiconductor device, flip-chip mounting has been used for so-called surface emitting devices that emit light in the vertical direction from a substrate, for example, light emitting diodes (Non-Patent Document 2). FIG. 9 is an example. The surface light emitting diode 110 includes a p-electrode 115, a p-GaN layer 114, an active layer 113, an n-GaN layer 112, and a sapphire substrate 111 on a wiring board 118 via gold bumps 117. An n-electrode 116 is provided at the end. A current is injected into the surface light emitting diode, and the current flows from the p-electrode 115 toward the n-electrode 116. Here, the gap between the wiring board 118 and the p-electrode 115 and the n-electrode 116 is filled with an adhesive such as epoxy resin. Since light is emitted in the vertical direction from the sapphire substrate 111, no problem occurs even if the adhesive leaks out and hits the end face.

  However, in the surface light emitting device, since the active layer portion cannot generally be made long, the light output is generally insufficient. For example, a light source for optical communication of medium and long distances requiring a modulation average output of 0 dBm or more is used. Cannot be used. A so-called edge-emitting device that emits light in a direction parallel to the substrate is essential for a light source for medium-long distance optical communication.

  Non-Patent Document 3 describes a direct modulation DFB laser corresponding to flip-chip mounting. FIG. 3 is a diagram showing a configuration of a two-channel optical transmitter for flip chip mounting. In the optical transmitter of FIG. 3, the DFB laser array 16 with a multiplexer shown in (a) and the high-frequency wiring board 25 mounted on the carrier 40 shown in (b) are connected by a gold bump 42 and an adhesive 41. Thus, it is configured as shown in (c) and (d).

  When flip chip mounting is performed, the gold bump 42 provided on the modulation electrode alone is insufficient in strength. Therefore, the GND electrode 15 is separately provided, and the gold bump 42 is also provided on the GND electrode 15 to support the optical semiconductor element. It is desirable to do. Therefore, the laser array 16 in FIG. 3B has a configuration in which a ground electrode 15 is formed on the substrate growth surface side of the laser array 10 in FIG. The high frequency distribution board 25 shown in FIG. 3B is provided with a high frequency wiring line 21 and a GND 22 for applying a high frequency signal to two DFB lasers.

  As shown in FIG. 3C, first, the DFB type laser array 16 with a multiplexer shown in FIG. 3B is mounted on the subcarrier 30 and then turned upside down (with the crystal growth surface facing down). The laser array 16 is mounted on the high-frequency wiring board 25 using gold bumps 42. The gold bumps 42 are disposed on the DFB laser modulation electrode 11 and the GND electrode 15. The gap between the gold bumps is filled with an adhesive 41.

  The problem here is that the overflowing adhesive wraps around the end face of the semiconductor chip. Since the adhesive is an insulator, there is no problem even if it goes around the end face of the electronic device, and no problem arises for the surface emitting device. However, for the edge-emitting device, when it goes around the front surface, the refractive index of the non-reflective coatings 13 and 14 changes and the reflection characteristics change, so that light is reflected at the edge. As a result, various adverse effects such as fluctuation of the oscillation wavelength of the semiconductor laser, deterioration of the eye pattern, fluctuation of the light output intensity, and the like occur. In the first place, since the light emitted from the end face is obstructed, the light output intensity may be reduced or no light may be emitted at all.

  Even if it wraps around the back surface, the properties of the non-reflective coating will change, and light reflection will occur at the end surface, which causes fluctuations in the oscillation wavelength of the semiconductor laser, deterioration of the eye pattern, and light output. Various adverse effects such as fluctuations in strength occur. FIG. 3D illustrates an example in which the adhesive wraps around the rear surface, but it may wrap around the front surface or may wrap around both the front surface and the rear surface.

  The same applies to the EADFB laser module. The semiconductor chip 55 shown in FIG. 4A has a configuration in which a GND electrode 53 is formed on the crystal growth surface side of the semiconductor chip 50 of FIG. Similarly to FIG. 3, when the semiconductor chip 55 shown in FIG. 4A is flip-chip mounted on the high-frequency wiring board 27 of FIG. 4B, the wraparound of the adhesive to the end surface becomes a problem.

  As described above, the normal flip chip mounting technique has a problem that it cannot be applied to an optical semiconductor element in which light is emitted and incident from the end face because the adhesive used at the time of fixing wraps around the end face of the chip.

  The present invention has been made in view of the above conventional problems, and an object of the present invention is to realize an optical semiconductor module capable of operating at high speed using an optical semiconductor element in which light is emitted and incident from an end face. .

  In order to solve the above-described problems, an invention described in one embodiment is a flat optical semiconductor element having a high-frequency wiring board and a crystal growth surface disposed so as to face the high-frequency wiring board. An optical semiconductor element that inputs or outputs light from at least one of the four end faces, and a gold bump and an adhesive for electrically connecting and fixing the optical semiconductor element on the high-frequency wiring board An optical semiconductor module comprising a fixing means including the optical semiconductor element, wherein the optical semiconductor element has a flow stop portion for the adhesive in the vicinity of an end surface of the crystal growth surface, and the optical axis of the input or output light The length of the optical semiconductor element in the direction is longer than the length of the high-frequency wiring board.

It is a figure which shows the structural example of the direct modulation | alteration DFB laser array module of the conventional wire mounting. It is a figure which shows the structural example of the conventional wire mounting EADFB laser module. It is a figure which shows the structural example of the direct modulation | alteration DFB laser array module of the conventional flip chip mounting. It is a figure which shows the structural example of the EADFB laser module of a conventional flip chip mounting. It is a figure which shows the structural example of the direct modulation | alteration DFB laser array module of the flip chip mounting of this invention. It is a figure which shows the structure of a part of direct modulation | alteration DFB laser array for flip chip mounting used by this invention. It is a figure which shows the structural example of the EADFB laser module of the flip chip mounting of this invention. It is a figure which shows sectional drawing of an EADFB laser. It is a figure which shows the example of the flip chip mounting of the conventional surface emitting device.

  Hereinafter, embodiments of the present invention will be described in detail.

  The optical semiconductor module according to the present embodiment will be described with reference to an example in which a multiplexer integrated two-channel direct modulation DFB (distributed feedback distributed feedback) laser array chip is used. FIG. 5 is a diagram illustrating a configuration example of the optical semiconductor module. 5A is a top view of a plate-like laser array chip (also referred to as an optical semiconductor element or chip) 1, FIG. 5B is a side view showing the configuration of the optical semiconductor module, and FIG. It is a top view of (b). As shown in FIG. 5A, the optical semiconductor module of the present embodiment can be configured by using a laser array chip 1 in which an adhesive flow stop portion 2 is disposed in the vicinity of the end face of the crystal growth surface. The laser array chip 1 has basically the same configuration as that of the chip 10 of FIG. 3 except for the adhesive flow stop portion 2.

  Further, as shown in FIG. 5B, in the optical semiconductor module, the high-frequency wiring board 25 and the laser array chip 1 are fixed via gold bumps 42 that are electrical connectors and an adhesive 41 that is an electrical insulator. It has a configuration. In the optical semiconductor module, the length of the laser array chip 1 is formed longer than the length of the high-frequency wiring board 25 in the optical axis direction (right direction in the drawing), and the chip 1 is fixed so as to protrude to both sides of the high-frequency wiring board 25. ing. By adopting such a structure, even when the crystal growth surface of the laser array chip 1 is mounted downward (in a direction facing the high-frequency wiring board 25), the adhesive 41 flows around the end surface at the adhesive flow stop portion 2. In addition, the surplus adhesive 41 also flows down from the high-frequency wiring board 25, so that the fixing adhesive 41 does not go around the light-exited end surface portion, so that flip chip mounting is possible. By adopting the above configuration, an optical semiconductor module capable of high-speed operation can be realized.

  Hereinafter, a specific embodiment of the present invention will be described as an example. This embodiment is an example showing the effect of the present invention, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

  The configuration of this embodiment is shown in FIG. In the present embodiment, a multi-channel integrated two-channel direct modulation laser array 1 is used as an optical semiconductor element. The adhesive flow stop part 2 is formed by plating at the time of chip manufacture. Further, gold bumps 42 were used for the electrical connection parts, and an adhesive 41 made of epoxy resin was used for the electrical insulation parts, and a terminal resistor was made on the wiring of the high-frequency wiring board 25. However, the terminating resistor is omitted in the drawing. The laser length was 0.2 mm.

  FIG. 6 shows an element structure of a part (one channel) 1a of a direct modulation DFB laser. FIG. 6 is for explaining the layer structure of the element, and the adhesive flow preventing portion 2 is not shown. This structure is intended for differential operation of the DFB laser, and the GND electrode 15 is formed on the same surface (crystal growth surface) as the modulation electrode 11. That is, the semiconductor element can be supported using not only the gold bump on the modulation electrode 11 but also the gold bump on the GND electrode 15.

  In addition, a semi-insulating InP substrate 106 is used for electrical separation between the DFB lasers. An n-GaInAsP contact layer 105, an n-InP clad layer 108, a GaInAsP active layer 104, a p-InP layer 102, and a p contact layer 101 are grown on a semi-insulating InP substrate 106, and a mesa is formed. Embedding. A separation groove D1 was formed in order to separate the modulation electrode 11 and the GND electrode 15 of the DFB laser, and an electric separation groove D2 was formed in order to obtain electrical separation between the DFB lasers. The modulation electrode 11 of the DFB laser was 50 × 50 microns.

1. Assembly Process Referring to FIG. 5, a procedure for actually manufacturing this module will be described. The adhesive flow stop portion 2 was formed by gold plating when the laser array chip 1 was manufactured, and the height was 25 μm.

  First, the laser array chip 1 is mounted on the subcarrier 30. Next, gold bumps 42 are formed on the DFB laser electrode 11 and the GND electrode 15 by a ball bonder. The gold bump 42 has a height of about 30 μm. Then, the laser array chip 1 is flip-chip mounted on the high-frequency wiring board 25 mounted on the carrier 40 with the gold bump mounting surface (crystal growth surface) facing down. At this time, the gold bumps 42 and the high-frequency wiring board 25 were joined with ultrasonic waves. Finally, an epoxy resin adhesive 41 is poured from the side surface of the chip 1 and fixed. Thus, the laser array light source module as shown in FIGS. 5B and 5C is completed.

2. Characteristics of Module First, the appearance of the created module (FIGS. 5B and 5C) was confirmed, and it was confirmed that the adhesive did not wrap around.

  Next, frequency response characteristics were measured. As a comparison, measurement was also performed with the configuration of FIG. The measurement was performed by using a network analyzer, inputting an electrical signal through a high-frequency probe applied to a high-frequency wiring board, and inputting light received through the tip fiber into the network analyzer. 1A and 5A, the lower laser is channel 1 and the upper laser is channel 2. In FIG. As a result of measuring the frequency response characteristics with a bias current of 60 mA flowing in channel 1, the wire-mounted conventional type (comparative example, configuration of FIG. 1) was about 13 GHz in the 3 dB band, while the example In (configuration of FIG. 5), the 3 dB band was improved to 18 GHz.

  Finally, the current-light output characteristics were compared between the configuration of the example and the configuration of the comparative example. At this time, the temperature of the carrier was kept constant at 25 degrees. In addition, measurement was performed using channel 1. Both threshold values were about 10 mA, whereas the optical output at a bias current of 80 mA was 13 mW in the comparative example, whereas it was 14 mW in the example. This is considered to be due to the fact that the heat dissipation is improved by the structure of the embodiment shown in FIG. 5 and the active layer temperature is lower than that of the conventional type.

  From the above, it is apparent that an optical semiconductor module capable of high-speed operation can be realized.

  The configuration of this embodiment is shown in FIG. 7A is a top view of a plate-like laser array chip (also referred to as an optical semiconductor element or chip) 3, FIG. 7B is a side view showing the configuration of the optical semiconductor module, and FIG. It is a top view of (b). The laser array chip 3 basically has the same configuration as that of the semiconductor chip 55 of FIG. 4A except for the adhesive flow stopper 4 provided in the same manner as the laser array chip 1 of FIG. Yes.

  In this embodiment, an EADFB laser is used as the optical semiconductor element (laser array chip) 3. The adhesive flow stopper 4 is formed by mounting an alumina substrate having a height of 0.1 mm during mounting. Further, gold bumps 42 were used for the electrical connection parts, and an adhesive 41 made of epoxy resin was used for the electrical insulation parts. However, the terminating resistor is omitted in the drawing. The EA length was 0.15 mm, and the DFB laser length was 0.5 mm.

  FIG. 8 is a diagram for explaining the layer structure of the EADFB laser shown as the laser array chip 3 in FIG. In the figure, an n-electrode 301, an n-InP substrate 302, and an n-InP cladding layer 303 are stacked, and in a region functioning as a DFB semiconductor laser region, a semiconductor laser is placed on the n-InP cladding layer 303. An active layer 304 and a semiconductor laser guide layer 305 are stacked. A diffraction grating is formed on the guide layer 305 by EB (electron beam) drawing. Further, a p-InP clad layer 306 is laminated, and a semiconductor laser electrode 307 is provided. In the region functioning as the EA modulator, an absorption layer 308 of the EA modulator and a p-InP cladding layer 306 are stacked on the n-InP cladding layer 303, and an electrode 309 of the EA modulator is provided. ing. Further, in the region functioning as the waveguide and the optical multiplexer, the core layer 310 of the waveguide (or the optical multiplexer) and the non-doped InP 311 are stacked on the n-InP cladding layer 303.

  In the central portion of the DFB semiconductor laser, a quarter wavelength shift 312 is provided by shifting the phase of the diffraction grating by a quarter wavelength in order to realize a single mode of the oscillation wavelength.

1. Assembly Process Referring to FIG. 7, a procedure for actually manufacturing this module will be described. First, the laser array chip 3 is mounted on the subcarrier 30. Next, an alumina substrate is fixed as an adhesive flow stop part 4 on both sides near the end face of the crystal growth surface of the laser array chip 3 using polyurethane resin. Next, gold bumps are formed on the DFB laser electrode 51, the EA modulator electrode 52, and the GND electrode 53 by a ball bonder on the crystal growth surface of the laser array chip 3. The gold bump has a height of about 30 μm. Then, the laser array chip 3 is flip-chip mounted on the high-frequency wiring board 27 mounted on the carrier 40 with the gold bump mounting surface (crystal growth surface) facing down. At this time, the electrode 51 of the DFB laser part is also connected to the DC wiring on the high-frequency wiring board 27 through the gold bump 42. The gold bumps 42 and the high-frequency wiring board 27 were joined by thermocompression bonding. Finally, the polyurethane resin adhesive 41 is poured from the side surface of the chip 3 and fixed. The EADFB laser module as shown in FIGS. 7B and 7C is thus completed.

2. Module characteristics First, the appearance of the module was confirmed, and it was confirmed that the adhesive did not wrap around.

  Next, frequency response characteristics were measured. As a comparison, measurement was also performed with the configuration of FIG. The measurement was performed by using a network analyzer, inputting an electrical signal through a high-frequency probe applied to a high-frequency wiring board, and inputting light received through the tip fiber into the network analyzer. As a result of measuring frequency response characteristics with a DFB laser bias current of 60 mA and an EA modulator bias voltage of −1.8 V, the conventional wire-mounted type (comparative example, configuration shown in FIG. 4) has a frequency of 25 GHz in a 3 dB band. On the other hand, in the example (configuration of FIG. 7), the 3 dB band was improved to 33 GHz.

  Finally, the current-light output characteristics were compared between the configuration of the example and the configuration of the comparative example. At this time, the temperature of the carrier was kept constant at 25 degrees. Both threshold values were about 20 mA, whereas the optical output at a bias current of 80 mA was 30 mW in the comparative example, whereas it was 35 mW in the example. This is considered to be due to the fact that the heat dissipation was improved by the structure of the embodiment shown in FIG. 7 and the active layer temperature was lower than that of the conventional type.

  From the above, it is apparent that an optical semiconductor module capable of high-speed operation can be realized.

  In the above description, an optical semiconductor chip that outputs light only in one direction has been described as an example. However, an optical semiconductor chip that outputs light to both end faces may be used.

  Alternatively, an input / output device (for example, a Mach-Zehnder modulator) that inputs light from one end face and outputs from the other end face may be used. Light input from one end face is reflected by the other end face and output from the same face as the input face. It is also possible to use a device (for example, a reflection type optical amplifier).

  Furthermore, it can also be applied to devices that emit light from the end surface, but output the surface (surface-emitting devices), and conversely, it can also be applied to devices that input the surface but output the surface. It can be applied to devices.

  Although the adhesive flow stopper is provided on both end faces of the element, a certain effect can be obtained even if it is provided only on one side. It goes without saying that the adhesive flow stop on the rear surface is not necessary particularly in the case of a structure in which no light is emitted from the rear surface (and therefore no antireflection coating is required).

1, 3 Laser array chip 2, 4 Adhesive flow stop part 25, 27 High-frequency wiring board 30 Subcarrier 40 Carrier 41 Adhesive 42 Gold bump

Claims (4)

A high-frequency wiring board;
A planar optical semiconductor element having a crystal growth surface disposed so as to face the high-frequency wiring board, wherein the optical semiconductor element inputs or outputs light from at least one of the four end faces;
An optical semiconductor module comprising a fixing means including a gold bump and an adhesive for electrically connecting and fixing the optical semiconductor element on the high-frequency wiring board,
The optical semiconductor element has the adhesive flow stop portion in the vicinity of an end face of the crystal growth surface, and the length of the optical semiconductor element in the optical axis direction of the input or output light is the length of the high-frequency wiring board. An optical semiconductor module, wherein the optical semiconductor module is formed longer than the length.   2. The optical semiconductor module according to claim 1, wherein the adhesive flow stop portion is provided in the vicinity of two end surfaces in the optical axis direction. 3.   The optical semiconductor module according to claim 1, wherein the adhesive is an insulating resin agent.   4. A GND electrode for mounting a gold bump for supporting an optical semiconductor element is disposed on an upper surface of the optical semiconductor element that contacts the high-frequency wiring board. An optical semiconductor module according to 1.

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